‘Serious leisure’ cycling has developed as a reinterpretation of the traditional form of the sport. This short term, informal, unstructured and unconventional conceptualisation represents a challenge to participant numbers in the mainstream sport. The purpose of this study was twofold: (i) to ascertain the cultural, subcultural and ecological factors of participation in this new conceptualised form enabling clubs, associations and governments to a deeper understanding about participants practices and (ii) as an ongoing validation to previous qualitative work (see O’Connor and Brown, 2005). This study reports on the development and psychometric properties (principal components analysis, confirmatory factor analysis) of the Cyclists’ Motivation Instrument. Four hundred and twenty two cyclists (371 males, 51 females) who were registered members of the state competitive cycling body completed a fifty-one item instrument. Five factors were identified: social, embodiment, self-presentation, exploring environments and physical health outcomes and these accounted for 47.2% of the variance. Factor alpha coefficients ranged from .63 to .88, overall scale reliability was .92, suggesting moderate to high reliability for each of the factors and the overall scale.